1. Field of the Invention
The present invention relates to an exhaust gas treatment device for purifying exhaust gas by bringing the exhaust gas into contact with seawater and also relates to a waste water treatment method for the exhaust gas treatment device.
2. Description of the Related Art
In thermal power plants, chemical industry plants, waste incinerator facility, and ship and vessel, there are used engines and boilers using fossil fuels. From these engines and boilers, exhaust gas is discharged containing sulfur (mainly (SO2), and for environmental conservation, this SO2 needs to be eliminated to a fixed level by an exhaust gas treatment device. The exhaust gas treatment device is a device that uses alkaline absorbent and brings exhaust gas into contact with alkaline absorbent in a scrubber (absorption tower) to absorb SO2 thereby to remove SO2 (wet desulfurization) (for example, see patent literatures 1 and 2).
In patent literatures 1 and 2, when SO2 in exhaust gas is removed, cleaning seawater is charged as alkaline absorbent into a scrubber, and this cleaning seawater absorbs SO2 thereby to produce waste water having a pH (hydrogen ion concentration) of about 3-5. This waste water is charged from the scrubber into a waste water treatment tank. In the waste water treatment tank, waste water is mixed with dilution seawater that is pumped up by a seawater pump, and then, a resultant is subjected to aeration treatment via a nozzle or the like. By this aeration treatment, pH in the waste water increases, and thereby, it becomes possible to discharge the waste water as quality-improved water into sea in a sea area excluding the Emission Control Area (ECA).
The following documents constitute related art with respect to the present invention:
Patent Literature 1: Japanese Patent Application Publication No. 2006-55779
Patent Literature 2: Japanese Patent Application Publication No. 2011-524800
However, in the methods disclosed in the patent literatures 1 and 2, the amount of dilution seawater becomes two to six times greater than the amount of cleaning water (see the report from United States Environmental Protection Agency announced in 2011, “Exhaust Gas Scrubber Wash Water Effluent”). Since this large amount of dilution seawater is pumped up and used, there arises a problem that the energy consumed for seawater pump becomes large. This problem is more significant particularly in ships and vessels because the energy available on ships or vessels in passage is limited.